When burning solid fuel in a fluid bed furnace the temperature is usually maintained at a moderate level of about 850.degree. C. In this manner a sinterning of the fuel residues is prevented, and the risk of generating certain obnoxious emissions, especially nitrogen oxide, NO.sub.x, is reduced. An increase of other environmentally harmful emissions, for instance N.sub.2 O (laughing gas) may instead be brought about. This is especially noticeable when burning bio-mass fuels.
The object of the present invention is to propose a device for the destruction of such gaseous emissions, which will occur during combustion at comparatively moderate temperatures in a fluid bed furnace.